A : polycom group700 ver5.1.2 1080p 4mp
B : lifesize team220 4mp
C : polycom group700 ver5.1.2 1080p
What is the problem??
Are they all on the same local network or going thru Internet or MPLS?
Have you looked at the CALL STATISTICS during a problem call?
Maybe the SYSTEM LOGS show something relating to video protocol/resolution negotiation.